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We report herein the development of a general and mild protocol of oxygen-promoted Pd(II) catalysis resulting in the selective cross-couplings of alkenyl- and arylboron compounds with various olefins. Unlike most cross-coupling reactions, this new methodology works well even in the absence of bases, consequently averting undesired homo-couplings. Nitrogen-based ligands including dimethyl-phenanathroline enhance reactivities and offer a highly efficient and stereoselective methodology to overcome challenging substrate limitations. For instance, oxidative palladium(II) catalysis is effective with highly substituted alkenes and cyclic alkenes, which are known to be incompatible with other known catalytic conditions. Most examined reactions progressed smoothly to completion at low temperatures and in short times. These interesting results provide mechanistic insights and utilities for a new paradigm of palladium catalytic cycles without bases.

Reported herein is a mild and efficient Pd(II) catalysis, leading to the formation of carbon-carbon bonds between a broad spectrum of organoboron compounds and alkenes. Molecular oxygen was employed to reoxidize the resultant Pd(0) species back to Pd(II) during catalytic cycles. This oxygen protocol promoted the desired Pd(II) catalysis, whereas it retarded competing Pd(0) catalytic pathways such as Heck or Suzuki couplings. [reaction: see text]

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Herein, we report an asymmetric intermolecular Heck-type reaction of acyclic alkenes by using a palladium-pyridinyl oxazoline diacetate complex under oxidative palladium(II) catalysis conditions. A premade palladium-ligand complex afforded higher enantioselectivities than a corresponding premixed palladium-ligand system, while offering enhanced asymmetric induction when compared to known intermolecular Heck-type protocols.

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Formal aromatic C-H insertion of rhodium(II) carbenoid was intensively investigated to develop a new methodology and probe its mechanism. Contrasting with the previously proposed direct C-H insertion, the mechanism was revealed to be electrophilic aromatic substitution, which was supported by substituent effects on the aromatic ring and a secondary deuterium kinetic isotope effect. Various isoquinolinones were synthesized intramolecularly via six-membered ring formation with high regio- and diastereoselectivity, while averting the common Buchner-type reaction. Intermolecularly, dirhodium catalyzed formal aromatic C-H insertion on electron-rich aromatics was also achieved.

+)-Di hydronepetalactone and (+)-iridomyrmecin were synthesized from the stereoselective Favorskii rearrangement product of (+)-cawone chlorohydrin.Functionalized cyclopentanecarboxylates are obtained from the Favorskii rearrangement of cyclohexanone derivatives, e.g., Favorskii rearrangement of the monoepoxide 1 of (-)-carvone afforded a highly functionalized cyclopentanecarboxylic acid 2 albeit in low yield' (Scheme 1).The stereochemical array in 2 requires cyclopropanone derivative 3 as an intermediate (presumably formed by the SN2 type displacement of the epoxide moiety) in which the selective cleavage of the bond between C-1 and C-2 is coupled with the stereoselective protonation at C-2 resulting in retention of the stereochemistry. We prepared the chlorohydrin derivative of (-)-carvone to examine Favorskii rearrangement. The Favorskii rearrangement of the chlorohydrin 4 is very efficient and provides a valuable cyclopentanecarboxylate derivative 5 , and its enantiomer 8 is converted into cat-a ttracting iridolactones ,2 ( + )-di hydronepe talactone 113 and (+)-iridomyrmecin 14.4